Most state schools spend just £1 per pupil each year on religious education, a new study claims.
The statistics were released as a preclude to the debate on Wednesday evening which focuses on the relevance of faith in schools.
According to research by James Conroy, professor of religious and philosophical education at Glasgow University, the subject is under-funded and lacking in time and resource.
His report, based on a study of 24 UK schools, warns RE lessons are becoming less about exploring issues of faith and now cover everything from citizenship to sex and relationships.
Conroy's paper is due to be presented at the second of the Westminster Faith Debates later on Wednesday, which is focusing on faith in schools.
Also taking part in the debate will be Richard Dawkins, former Charles Simonyi professor of the public understanding of science at Oxford University, John Pritchard, Bishop of the Anglican Diocese of Oxford and chair of the Church of England's board of education and Professor Robert Jackson, director of the Warwick Religions and Education Research Unit (WRERU).
Conroy's three-year study found that schools which offer good RE lessons have close links with their local community and are aware of its religious make-up.
Teachers are also willing to discuss with pupils the meanings behind different rituals and social and personal practices, the study says.
But it adds that in poor RE classes, teachers simply introduce students to the "surface phenomena of religion".
The report claims: "The problem goes much deeper than individual teachers or schools. It is symptomatic of a crippling ambivalence about RE which runs through British society, and infects educational policy."
Conroy said: "Even where RE is taught magnificently, it is so against the odds.
"RE in Britain is under-resourced, torn between competing aims, and has become overburdened by having to include other subjects (from sex to citizenship).
"Whilst governments insist on RE's importance in theory, they marginalise it in practice - as Michael Gove has recently done by refusing to treat it as a core subject and excluding it from the English Baccalaureate."
The study found: "In most state schools £1 or less is spent on each child per annum on materials and books for RE."
Even when pupils sit exams in RE, teachers are expected to teach the syllabus in less time than is allowed for other subjects, it said.
Conroy's report concludes: "Religious education matters as never before. We cannot understand our own culture without religious knowledge, let alone that of others.
"As religious and secular diversity increases, students need to be able to articulate their own beliefs, and engage seriously with those of others, as never before. Respect and social harmony depend upon it.
"What is happening to RE in our schools is a scandal for which we will have to pay a high price in years to come."
Once established, it is expected that the group will focus on protecting RE in schools and its value to young people.
A Department for Education spokesman said: "RE remains a statutory part of the school curriculum for every student up to 18. It is rightly down to schools themselves to judge how it is taught, but the English Baccalaureate will not prevent any school from offering RE GCSEs. We have been clear that pupils should take the GCSEs that are right for them and that we look to teachers and parents to help pupils make the right choice."
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